1. Field of the Invention
The present invention relates to a method for producing a porous diamond.
2. Description of the Related Art
Porous diamonds have been used in dies for drawing, sensors, electrode materials and the like, and such porous diamonds have been conventionally produced by a method in which an etching-resistant mask is formed on a diamond substrate through a resist application and exposure patterning; and then a selective etching is conducted by a dry etching method. An alternative known method, which may be used to form more minute patterns on a diamond substrate, is to draw a pattern using an electric beam instead of exposure patterning; this is followed by a dry etching treatment.
In addition to the above conventional methods, a processing method for diamonds in which a high intensity laser beam is projected onto a diamond substrate so that part of the diamond is evaporated and vaporized is also known.
However, the conventional method in which a pattern is transferred using a resist and exposure patterning is limited as to minuteness of detail, due to the diffraction limit of light. Further, in the electric beam depiction method, which can draw more minute patterns compared to the optical transferring method, drawing of a pattern requires a longer time, thereby causing a significant increase in the total cost. Moreover, all conventional patterning methods wherein a resist is used commonly require rather complicated steps of application of a resist, drawing of pattern, and removal of the resist. In addition, since the aspect ratio (depth of pore/opening diameter of pore) of the resist patterns formed in the convention methods is small, there is a problem in that it is difficult to process a structure having a large aspect ratio during subsequent dry etching.
Even in a method using a laser beam which does not require the complicated steps like application of resist, the resolution of the process is also restricted to about 1 micron because of the diameter of the laser beam.
It is, therefore, an object of the present invention to provide a method for producing a porous diamond having fine pores of high density without including such complicated steps as those that are necessary for the above-mentioned conventional methods.
To accomplish the above-mentioned object, there is provided according to the present invention, a method for producing a porous diamond comprising steps of: forming an anodized alumina layer, which functions as a mask, on a diamond substrate; and performing a plasma etching treatment to form pores on the diamond substrate, which pores having the same arrangement as those of the anodized alumina mask. More specifically, in the method according to the present invention, a mask of anodized alumina having a number of minute through holes which are orthogonal to the surface thereof is formed on a diamond substrate, and then a plasma etching treatment is performed to process the surface of the diamond substrate in such a manner that the ordered structure of the mask is transferred onto the surface of the diamond substrate. The term xe2x80x9cthrough holesxe2x80x9d refers to holes that go all the way through a substance, for example, an anodized alumina layer.
An inert gas, like argon, as well as a gas including oxygen, can be effectively used as a gas for etching in the method according to the claimed invention. The porous structure formed on a diamond substrate by a method according to the present invention depends on the form of anodized alumina used as a mask. It is known that anodized alumina has pores (i.e., through holes) of a uniform diameter which is within a range from 10 nm to 400 nm, and such diameter can be controlled by controlling conditions for anodic oxidation (anodization) and a process of post-treatment. Further, by selectively etching the bottom portion of an anodized alumina film which is called a barrier layer, the anodized alumina film can be formed into a thin film having through holes [H. Masuda and M. Satho, Japanese Journal of Applied Physics, vol. 35 P.L126 (1996)].
With the method according to the present invention, as described above, minute processing can be performed on a diamond substrate without requiring additional steps such as application of a resist, exposure to light, or removal of the applied resist.